In telecommunications systems it is common to find a rack of equipment modules which perform the different functions of the system, such as interfacing to subscriber lines and switching. Building an installation in the form of modules allows simpler upgrades or repairs of the installation, with just those parts of the installation requiring change being affected. Typically the modules are held in a case which provides mechanical support for the modules. The case may also have some form of backplane to which each module couples, the backplane providing a path to guide signals between modules.
The backplane may comprise a set of conductive tracks to guide electrical signals between modules. Alternatively, an optical backplane may be used if a high signal bandwidth is required or if immunity to electrical interference is required.
UK Patent Application GB 2,201,561A describes a data handling system comprising a set of modules which are releasably retained in a racking system. An optical data link connects the modules. The link comprises one or more light transmissive bars which span the racking, apertures in the racking allowing light to couple between the bars and the modules. A separate electronic backplane extends along the rear wall of the racking to provide power supply to the modules.
U.S. Pat. No. 5,091,985 describes a signal connecting device for establishing communication paths between units in a rack. An optical waveguide is supported on a rear wall of the rack in which the units are held.